1. Field of the Invention
The present invention relates to processes for the production of silicon-containing polyimides low in hygroscopicity, and their precursors. More particularly, the present invention relates to processes for the production of silicon-containing polyimide precursors having a viscosity most suitable to be applied and their cured silicon-containing polyimides low in hygroscopicity and high in heat resistance and capable of forming a coating having powerful adhesion.
2. Prior Art
Polyimide resins are conventionally used widely as protective materials or insulating materials in the field of electronic equipment, or adhesives in the form of films, or structural materials mainly from the point of view of their heat resistance. In some techniques, polyimide resins are often combined with other inorganic materials to form heat resistant films, coatings, or adhesives. In that case, adhesion to the base material is required, and as techniques of improving the adhesion, use of various copolymers with silicon compounds is suggested. For example, such copolymers are disclosed in Japanese Laid-Open Patent Application Nos. 143328/1982, 7473/1983, and 13631/1983, and Japanese Patent Publication Nos. 18372/1983, 32162/1983, and 32163/1983, and the present inventors also suggested such copolymers in Japanese Laid-Open Patent Application No. 287926/1986, and Japanese Patent Application No. 162018/1987.
On the other hand, one of the weak points of polyimide resins is that the hygroscopicity thereof is high, deteriorating the electric properties. In order to lower the hygroscopicity, various fluorine-containing polyimides are suggested as described in Japanese Laid-Open Patent Application Nos. 149916/1983, 180530/1983, 189122/1984, 104129/1985, etc.
The hygroscopicity of fluorine-containing polyimides described in Japanese Laid-Open Patent Application Nos. 149916/1983, 180530/1983, 189122/1984, and 104129/1985 mentioned above is decreased 1/several times to about 1/10 times as much as that of usual polyimides free from fluorine, so that the effect is obvious.
However, such compounds have such disadvantages that not only they are inferior in adhesion to glass or the like but they are also low in glass transition point so that the thermal expansion coefficient thereof at a temperature over the glass transition point is extremely high thereby limiting the range of their application.
On the other hand, some compounds described in Japanese Laid-Open Patent Application Nos. 143328/1982, 7473/1983, and 13631/1983, and Japanese Patent Publication Nos. 18372/1983, 32162/1983, and 32163/1983, and Japanese Laid-Open Patent Application No. 287926/1986 mentioned above are lowered in hygroscopicity, but the effect of lowering hygroscopicity is not so remarkable as that of fluorine-containing compounds, and they also have such disadvantages that the glass transition point is low, and the thermal expansion coefficient at a temperature over the glass transition point is conspicuously high. Thus, the prior art techniques are accompanied by various problems, and therefore development of polyimide materials low in hygroscopicity and high in adhesion have been desired.